The present invention relates to a hydraulic circuit for a dual clutch transmission for motor vehicles, comprising a first and a second clutch that can be hydraulically actuated and a first and a second pressure control valve for regulating the clutch pressure of the first and second clutches.
Such a hydraulic circuit is generally known, for example from DE 101 34 115 A1.
Dual clutch transmissions for motor vehicles have recently attracted particular interest. They are based on the fundamental concept of conventional manual shift transmissions, but have two disengaging clutches. One disengaging clutch connects an engine output shaft to a first transmission branch, which for example comprises gear stages 1, 3, 5, . . . . The second disengaging clutch connects the engine output shaft to a second parallel transmission branch, which for example comprises gear stages 2, 4, 6, . . . .
The outputs of the two transmission branches are connected to a common output shaft, which is connected to the driving wheels of the motor vehicle.
By overlapping actuation of the disengaging clutches, it is possible to carry out gear changes from one gear to the next in an overlapping manner without interrupting the tractive force. This makes dual clutch transmissions very comfortable. Since the power transmission takes place by frictional or positive engagement, a comparatively high efficiency can be achieved at the same time.
Dual clutch transmissions can generally only be operated in an automated manner. At the same time, special safety precautions have to be taken to avoid two gear stages being selected simultaneously and simultaneously subjected to loading via the disengaging clutches. This could lead to the wheel sets and/or disengaging clutches being destroyed. The disengaging clutches are in this case generally hydraulically controlled clutches. To be precise, the disengaging clutches may be formed as dry clutches. However, it is advantageous if the disengaging clutches are formed as wet clutches, in particular as wet multi-plate clutches.
DE 101 34 115 A1, cited at the beginning, discloses a hydraulic circuit for the hydraulic control of a dual clutch transmission. In this case, the hydraulic circuit has a first partial circuit for the first disengaging clutch and the first transmission branch and a second partial circuit for the second disengaging clutch and the second transmission branch. The partial circuits are respectively connected on the input side to a hydraulic supply via release valves. The release valves are in this case formed as “failsafe” valves. In normal operation, the release valves are electrically released. In the event of failure of the electrical control, the release valves are moved by springs into a disengaging position, in which the partial circuits are disengaged from the hydraulic supply. At the same time, the partial hydraulic circuits are depressurized by connecting them to a tank. As a result, the two disengaging clutches are opened. In the case of such a malfunction, the vehicle consequently coasts and then comes to a standstill.
DE 101 38 395 A1 discloses an emergency actuating device for an automated controllable clutch which is designed such that it can be passively closed. In this case, the emergency actuating device has a pressure accumulator as an auxiliary energy store for emergency actuation.
Furthermore, DE 101 20 882 discloses the use of an arrangement comprising two check valves and a pressure limiting valve to prevent a pressure acting on the clutches from exceeding a maximum value.